1. Field of the Invention
The present invention relates to an electrostatic capacitance sensor, an electrostatic capacitance sensor component, an object mounting body and an object mounting apparatus, and more particularly, to an electrostatic capacitance sensor which is a nearby-object detecting sensor utilizing a variation in electrostatic capacitance and which can be utilized for an FA (Factory Automation) device, an inspecting device, a robot, a semiconductor manufacturing apparatus and the like, an electrostatic capacitance sensor component for such an electrostatic capacitance sensor, an object mounting body including such an electrostatic capacitance sensor component, and an object mounting apparatus having such an electrostatic capacitance sensor.
2. Description of the Related Art
FIG. 15 shows a sensor and a front stage of an amplifier of a conventional electrostatic capacitance nearby-object detector described in Japanese Patent Application Laid-open No. H7-29467. In FIG. 15, a sensor 111 comprises a three-layer printed substrate 112. A first layer pattern formed on one face of the printed substrate 112 is a detecting electrode 112a disposed to be opposed to an object detecting region. An inside pattern of the printed substrate 112 is a second layer pattern for shielding the detecting electrode 112a, i.e., an in-phase shield pattern 112b. A third layer pattern formed on the other face of the printed substrate 112 is a shield earth pattern 112c. The shield earth pattern 112c is a pattern for reducing an influence of noise from outside acting on the detecting electrode 112a and the in-phase shield pattern 112b. The patterns 112a and 112b are respectively connected to a core wire and a coated wire of the shield cable 113, and connected to a side of a main circuit 114. In the main circuit 114, the core wire to which the detecting electrode 112a is connected is connected to an input terminal of a buffer circuit 115. An output terminal of the buffer circuit 115 is connected to the coated wire of the shield cable 113, and connected to an input terminal of a Schmitt trigger circuit 116. A feedback resistance R is connected between an output terminal of the Schmitt trigger circuit 116 and an input terminal of the buffer circuit 115.
If a grounded object approaches the detecting electrode 112a, an electrostatic capacitance Cd therebetween is increased. The buffer circuit 115 and the Schmitt trigger circuit 116 constitute an oscillation circuit 117 which oscillates with the electrostatic capacitance Cd and the feedback resistance R as the time constant components, and an output of the oscillation circuit 117 is connected to a periodic counter 118. The periodic counter 118 measures an oscillating period of the oscillation circuit 117, and an output of the periodic counter 118 is applied to a linearizer 119. The linearizer 119 linearizes a periodical variation to be a variation in a distance to the object. An output of the linearizer 119 is input to a display circuit 120 and a comparison circuit 121. The comparison circuit 121 discriminates input signals with respect to a predetermined threshold value, and a judging signal indicative of whether there exists an object is output from an output circuit 122.
According to the above structure, since the detecting electrode 112a and the in-phase shield pattern 112b are connected to the input and output terminals of the buffer circuit 115 through the shield cable 113, the detecting electrode 112a and the in-phase shield pattern 112b are always at the same phase and same voltage. Therefore, the detecting electrode 112a does not receive an influence of the electrostatic capacitance between the detecting electrode 112a and the in-phase shield pattern 112b. Thus, a sensor section having the detecting electrode and an electronic circuit section can be separated from each other by the shield cable 113.
As described above, according to Japanese Patent Application Laid-open No. H7-29467, the sensor comprises the first layer pattern 112a of the detecting electrode for detecting the object, the second layer pattern 112b for the shield, and the grounded third layer electrode pattern. The amplifier and the detecting electrode are connected through the shield cable 113, and the separate ground wire is provided. This structure has the following problems:
(1) This structure requires a detecting electrode wire, a shield wire and a grounding wire, and the structure is complicated and the cost is increased.
(2) This structure requires a detecting electrode, a shield electrode and a grounding electrode, and the structure is complicated and the cost is increased.